Vibration damping device



April 25, 1950 JACKSON 2,505,120

' VIBRATION DAMPING DEVICE Filed Jan. 15, 1945 INVEN OZ Y wa 5 WQEWL/Z ATTORNEY Patented Apr. 25, 1950 VIBRATION DAMPING DEVICE Melvin F. Jackson, Racine, Wis., assignor to J. 1. Case Company, Racine, Wis., a corporation of Wisconsin Application January 15, 1945, Serial No. 572,845

- Claims. 1

This invention relates to improvements in vibration-damping tractor drives.

It is a primary object of the invention to reduce or eliminate tooth chatter in a tractor drive. The drive is one in which the tractor engine transmits its power to a cross shaft upon which the change speed gearing is located.

In a system of this character, a substantial mass in the form of a flywheel is coupled directly to a driving gear through the usual friction clutch. Also in the cross shaft there is a substantial mass in the form of the fixed change speed gears. A belt pulley is commonly fixed with this cross shaft and a driven gear on the shaft is meshed with the above mentioned driving gear, the usual backlash being present. All of the parts are made of highly resilient material and the possibility exists of repeated impact loads on the teeth of these gears due to a vibration of one or the other shaft to the extent of the backlash plus a torsional or other springing of the connected gears and shafts. The mass on one shaft acts as a base or anvil for the impacts delivered by the mass on the other shaft. This vibration may build up suificiently to cause a disagreeable noise and possibly to impose excessive loads on the gears or the shafts or both.

Obviously, it is undesirable to unnecessarily load the parts in this manner, and accordingly a further object of the invention is to reduce or eliminate. such vibration and withit such unnecessary loads. The action is most likely to occur at light loads. In fact, under heavy loads, which definitely eliminate the backlash, the chatter does not occur.

According to the present invention, a pulley is so mounted on the driven cross shaft as to have a limited amount of torsional movement with respect to the shaft, such movement being utilized to establish forces for damping the vibration of the shaft. The nature and objectives of the invention will appear more particularly from the following disclosure thereof.

In the drawings:

Fig. l is a diagrammatic plan view of a tractor drive embodying the invention.

Fig. 2 is an enlarged detailed view showing in perspective the separate component parts of my improved vibration damping pulley. a

Fig. 3 is a detailed view of the pulley in longitudinal section taken on line 33 of Fig. 4.

Fig. 4 is a view taken in transverse section on the line 4-4 of Fig. 3.

Like parts are identified by the same reference characters throughout the several views. I

The tractor prime mover 5, usually comprising meshed. The pinion portion l2 on cross shaft ll drives the differential gear set I3 which couples shafts M and i5 differentially. Chains or the like at It, ll connect the respective shafts l4, I5 with rear axle shafts l8, is to operatethe wheels.

The pulley at the end of cross shaft) is 'a combination power takeoff and vibration-damping device. The pulley is connected to an outer hub element 2i which is rotatably sleeved upon an inner hub element 22 keyed to the shaft l0, Hub element 22 has a shoulder at 23 against which hub element 2| is held by thrust disk 24 bolted to hub element 22. lhus hub element 2| is constrained against axial or universal movement of any kind and is permitted only rotative or torsional displacement with respect'to hub element 22 and shaft l0.

Relative rotation of pulley 20 and hub element 2| respecting the inner hub element 22 and shaft I0 is limited in two ways, one of which is impositive and the other positive. The cylindrical bearing surface 25 of the outer hub element 2| and the complementary cylindrical bearing surface 26 of the inner hub element 22 have registering, axially extending channels 21, 28 in which are disposed small dowel-shaped elastic keys 30 which yieldably transit motion between the inner and.

outer hub elements. The relative yielding between such elements is positively limited by the driving pins 32 which project axially from the outer hub element 2| into the sockets 33 bored into or through the shouldered base 23 of the inner hub element 22. Obviously, the pins may be in either the outer or inner hub element and the sockets therefore in the other. The elastic keys at 32 keep the respective pins yieldably centered in the respective sockets. The resistance to displacement is determined in part by the relative hardness of the elastic material of which the keys are made. This will ordinarily be natural or artificial rubber of any suitablehardness. The

range of relative circumferential movement between the inner and outer hub elements is determined by the circumferential clearance between the driving pins and their respective sockets and should be greater than the amplitude of the forced vibration as measured at the socket.

;:.b,0ll11d or vibratory motion of ,the parts. amount of ...energy.- involvedl-isevery slighu but the throes developed,:.owing to. theinertia and im- -zpactiefiectspcan beivepy ,large-.and the;novel -initterposition 0f :the simple gener-g-y absorbing unit Advantage is taken of the well known property of internal friction common to rubber and rubber-like materials for absorbing energy so as to cut downor inhibit, instead of to enhance or build up the rapid alternate twisting distortion common to highly resilient machine parts. The disclosed Iarrangementis characterized bya pair of substantial rotativezmasses connected to. each other by a system of highly resilient shafts involving a lost motion connection. While theeac tion is perhaps not completely understood, observations indicate that such systems oan be set into substantial torsional vibrationbyanyivariations in rate of driving oftone'massisuch foreex- .ample as the well known cyclic fluctuations in 1 speed of an internal combustion en ine, provided that the load is light 'enoughsothat the driven member may overrun the drivingimember during the low speedzperiods thereof to the ex- ;.tent.of.the.1ost motion. .Attheconclusion vofthe .overrun, an impact results which, ,due to the ,re-

J...silient;character of the partsan'd the inertia of ith tdriven ,mass, causes a rebound in a, direction .sqpposeditotherotation. While thedriven memjiher doesnot actuallyreverseits rotation, it does 83 behind the driverto ,theextent of the 10st emotion, ,whereupon-ianother impact results, this ztime donuthe drivingsideofi the lost motion. This i'. action may repeat itselfseveral times during vmach acceleration icycle of the driver, which in tcommontypesofeen ines occurstwice duringeach crevolution Qfithe cranhzshait.

The invention in its broader aspects comprises the (introduction into -a;system1of thisacharacter niofrian emirgmabsorbingunitor substance todis- :2

, iIJEtBrSOHIB .zof the energy present in the re- The {01' device :between the lost-emotion connectionein .ithi-S instance,:.the:;backlash in-1thegears and;one

- ':of the masses,- results rim a virtnallyicomplete elimination of the chatteringsefiect.

- {With ithisydevice in .use upon :the cross shaft at-IJ a the; pulley, l instead ofeamplifying the torque wibration inf'shaft 1 0, or increasing' -the impact :exerted on :the gear *teeth ;asa :result .of such @wvibration; tends :to-idamp the :vibrationgbeingpartticula-rly efiective ::as.-:a damping-agent :when the load is light. Whenever the pulley 29 is in use, the resistance or =-load to which its periphery is subjected will almost immediately overcome the resiliency of the --yieldable driving-keys 30 and the'torque will-be transmitted through the posi- -'-t-ive' driving connection aiiorded by the pins 132. '{As previously indicated, there is little or no "torque Wibrationinshaftl ll'whenitheshaft is under load. QGonsequently, the driving ,pulley functions for non-yielding motion transmission under .load

---when':its; damping effectis not required, but per- "forms its .dampingfunction at all other times.

I'Iclaim: ;1,.-i'I ,n 81'.'t13,017 1; lil/, .t.h9 :oihhiiiation with a ,tnr me nover having a drive shaft subject \to :itornne vibration, .of ,-a .;driv,en shaft, gears .op- .er -ativ ely connecting ,said "shafts, land ..means .on

4 sections, and elastically yieldable driving means resisting such oscillation.

2. The combination set forth in claim 1 in which the respective hub sections of the pulley are provided with positive driving connections affording a limited degree of lost motion within which .,the ielastically yieldable driving ,means is efifective.

3. The combination set forth in claim 1 in which one of said sections is apertured and the other provided with a pin loosely fitted to said aperture to provide a positive driving connection .,betwe.en,. said sections, the loose fitting of the pin ,jn'the,.,apertu 1e,providing a limited lost motion betweenesaidesections within which said elastic drivingmean i effective.

In-a-tractor *d-rive, the combination with an vinternal.combustion engine having a drive shaft subject to torque vibration, of a first cross shaft, 1a second crossshaft, drivinggearing between the cross shafts, driving. gearing from the engine .shaittothe,firstcrossshaitam a tractor pro- ,pellingjdrivc 'fromithe second cross shaft, toether with .a ,pulleyihaving means mounting it upon saidfirstcrossshaft in ,spacedrelation to the second mentioned drivingv gearing, saidmeans comprisinga vibration damper including means for permitting .a limited relative movement between h ,.p 1ey andithe firsticrcss shaft, and

elastically yieldable ,means ,res'iliently opposing .suchrelative movement.

5, ,In a. tractor,drivecoinprising an engine hav- ;ing,,a..driving, shaf.t, a gear. on the driving sh t .a-,d1'ivenegca-r meshing with .the first .mentioned ,gear, and aldriven shaft connected with the driven gear, :the combination with such driven ashaft ,;-of -.a combination pulley and vibration lingamatingbearing means for ac" i 1 ioscillaticn between said elements, and e1 yieldable: meansa o pp.osing1,-such oscillation.

idamperz in spacedz-reiationtosaid gears for relieViQgSaid gears of vibration chatter, comprising erdrivingy hub element to which the driven 'shaf-tis, connected, a, driven hub element town the ,pulleylis connected, said hub 6. The combination-set forth in claim '5 Lin .ifurther combination awith 1 means for positively limiting the :extent of oscillation between said eratively-=engaged between said "elements.

.elements.

' '7. ".The'device of-clairn 5 in Which:' the resiliently vyieldable means "opposing relative osc'illat -i tween-said elementsoomprises a rubber lzey opacter such thatanatiuial vibration ireoliency "ltheidrivenshaft iorrelieving, said gears, of vibra- .tion. chatter,. said means comprising a, pulley on sa i'd .,driven shaft spaced from said .gears and ohaving inner and outer-,hubsections, one .ofgsaid .sections:.beinggliastto thegshait and the other to the pulleyisaids-sections,having. respective mounte ings for limited relative oscillation between said .o f..on.e'; shaftmay' substantially c in nd wi h *that ofQthe other wherebyreboundand conseq lent.Yibrationlcha'tter ,mayidevelop between the teeth of the gearing to the extent of the'limits idefined bynaid backlash, .means on .the driven shaft forflrelieving @said gears tofgsaid vibration whatterrfiaid ,means comprisinga rotatablei mass "on said driven shaft spaced from said gears and having at least two independent sections, one of said sections being fast to the shaft and the other free to rotate relatively thereto, said sections being connected for limited relative oscillation, and an energy absorbing elastic connection between said sections yieldably resisting such oscillation for absorbing from oscillatory vibrations of said shaft enough energy to damp said vibrations.

10. In a tractor drive the combination with a prime mover having a drive shaft subject to torque vibration, of a driven shaft, gears operatively connecting said shafts and subject to backlash, a rotatable mass on each shaft of a character such that a natural vibration frequency of one shaft may substantially correspond with that of the other whereby rebound and consequent vibration chatter may develop between the teeth of the gearing to the extent of the limits defined by said backlash, means on the driven shaft for relieving said gears of said vibration chatter, said means comprising a rotatable mass on said driven shaft spaced from said gears and having at least two independent sections, one of said sections being fast to the shaft and the other free to rotate relatively thereto, said sections being connected for limited relative oscillation, and an elastic connection between said sections yieldably resisting such oscillation for so modifying the vibration characteristics of said driven shaft as to substantially prevent such correspondence of frequency and to avoid rebound between said gear teeth.

MELVIN F. JACKSON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

